Electroless copper plating solution and process

ABSTRACT

A plating solution suitable for the electroless deposition of copper on ferrous metal surfaces which comprises an aqueous acidic solution containing copper ions; chloride, bromide, or iodide ions; a polyalkylene glycol; and a tertiary amine compound of the structure:

Hacias 14 1 Feb. 19,1974

1 1 ELECTROLESS COPPER PLATING SOLUTION AND PROCESS [75] Inventor: Kenneth J. Hacias, Sterling Heights,

Mich. l

[73] Assignee: Oxy Metal Finishing Corporation,

Warren, Mich.

[22] Filed: Mar. 13, 1972 [21] Appl. No.: 234,302

Primary Examine r Lorenzo B layes v P Attorney, Agent, or Firm-Wi11iam J. S chramm:

[57] ABSTRACT A plating solution suitable for the electroless deposition of copper on ferrous metal surfaces which comprises an aqueous acidic solution containing copper ions; chloride, bromide, or iodide ions; 3 polyalkylene glycol; and a tertiary amine compound of the structure:

, a lb wherein:

a is zero or 1;

b is 2 or 3;

a b is 3;

n is 0 to 4, inclusive; or substituted alkyl R is alkyl/of 1 to 4 carbon atoms where the substituent may be hydroxy or halo; and,

R is phenyl or substituted phenyl where the substituent may be mono-, di-, or trihalo or alkyl of 1 to 4 carbon atoms.

ELECTROLESS COPPER PLATING SOLUTION AND PROCESS BACKGROUND OF THE INVENTION This invention relates to a novel composition and process for the treatment of metal surfaces and more particularly it relates to a composition and process for the electroless copper plating of ferrous metal surfaces.

While many of the compositions and processes which I have heretofore been developed have been generally satisfactory, some difficulties have been encountered where different types and grades of ferrous metal surfaces have been treated. Frequently, with the compositions and processes of the prior art, variations in the type of ferrous metal being treated have resulted in similar variations in the quality of the copper coating which has been produced. Moreover, where these cooper coating solutions have been used for treating steel wire, prior to wire drawing operations, it has often been found to be difficult to consistently obtain a bright, adherent coating. Additionally, the compositions of the prior art have had relatively low tolerance for ferrous iron. With these solutions, as the quantity of ferrous iron in the bath has increased, the quality of the copper coating produced has decreased. It has, therefore, been the practice to discard the electroless copper plating solution when the ferrous iron content has built-up to about 3.5 to 4 percent Fe-H- and make up a new plating bath. This, of course, is'costly, both from the standpoint of the cost of the treating materials, as well as in the processing time lost while the line is shut down for the building-up of a new treating bath. Additionally, this frequent discarding of the bath adds greatly to waste disposal problems.

It is, therefore, an object of the present invention to provide an improved coating solution from which bright, adherent copper coatings may be obtained on a variety of ferrous metal surfaces, without the use of electric current. v r r a A further object of the present invention is to provide an improved process for forming a bright, adherent copper coating on a variety of ferrous metal surfaces without the use of electric current.

Another object of the present invention is to provide an improved composition and process for forming a bright, adherent copper coating on ferrous metal surfaces, which composition and process will tolerate the build-up of appreciable quantities of ferrous iron in the coating solution without adversely affecting the quality of the copper coating which is produced.

These and other objects will become apparent to those skilled in the art from the description of the invention which follows.

SUMMARY OF THE INVENTION Pursuant to the above objects, the present invention includes an aqueous acidic solution containing copper ions; halide ions selected from chloride, bromide and iodide ions; a polyalkylene glycol; and a tertiary amine compound having the formula:

u N M 2)" RIII;

wherein:

a is zero or l;

b is 2 or 3;

a b is 3;

n is 0 to 4, inclusive; or substituted alkyl R is alkyl/of l to 4 carbon atoms where the substituent may be hydroxy or halo; and

R is phenyl or substituted phenyl where the substituent may be mono-, di-, or tri-halo or alkyl of l to 4 carbon atoms.

DESCRIPTION OF PREFERRED EMBODIMENTS It has been found that various types of ferrous metal surfaces may be treated with this composition, without 20 the use of electric current, to form bright, adherent copper coatings on the ferrous metal surfaces. Moreover, these results are obtained even with a ferrous iron content in the bath at saturation point. This method is found to be particularly suited for the treatment of steel wire, prior to subjecting the wire to a drawing operation, as the copper coatings produced are found to retain their adhesion after the drawing operation.

More specifically, in the practice of the present invention, the novel plating solutions are aqueous acidic 30 solutions containing copper ions, which solutions desirably have a pH within the range of about 0 to 2, and preferably within the range of about 0.2 to 0.4. The copper ions are desirably present in the plating solutions in amounts within the range of about 0.1 to 3.0 percent by weight of the solution and preferably in an amount within the range of about 0.3 to 0.8 percent by weight of this solution. The copper ions may be incorporated in the plating solutions in any suitable form, such as copper metal, and/or various copper salts. The only requirements are that whatever form of copper is used, it will produce the aqueous acidic plating solution containing the desired copper ion content, within the desired pH range, and that the ions incorporated with the copper will not have any detrimental effect on either the solution and its operation or on the quality of the copper plate which is produced.

In many instances, it has been found to be convenient to utilize copper sulfate as the source of copper ions, in forming the aqueous acidic plating solutions. Additionally, with such baths, the bath pI-I may be maintained within the desired range by the addition of sulfuric acid. Where the aqueous acidic plating baths used contain such sulfate ions, they are typically present in amounts within the range of about 0.1 to 30. percent by weight of the solution. It is to be appreciated, of course, that other copper salts may also be used as the source of copper ions, such as copper chloride, copper bromide, copper acetate, copper citrate, copper benzoate, copper metaborate, copper butyrate, copper formate, copper sulfamates, and the like, and that other acids may be used for the pH adjustment of the bath. It is to be appreciated, however, that in using such other salts or acids, particularly those containing halide ions, care should be taken that the amounts of ,such latter ions introduced do not exceed the maximum amounts which can be present in the solution without detrimental effect.

As has been indicated, the plating solutions of the present invention contain halide ions, selected from chloride, bromide, and iodide ions. In many instances, however, the chloride ions are preferred; Where chloride ions are used, they are desirably present in amounts within the range of about 0.001 to about percent by weight of the solution and preferably in amounts within the range of about 0.01 to 0.5 percent. Where bromide ions are used, they are desirably present in amounts within the range of about 0.001 to 5 percent weight and preferably in amounts within the range of about 0.02 to 0.5 percent by weight of the solution, while the iodide ions, if ,used, are desirably present in amounts within the range of about 0.001 to 5 percent by weight and preferably in amounts within the range of about 0.01 to 0.2 percent by weight of the solution. These are desirably added as the alkali metal salts.

The polyalkylene glycol used'in the plating baths of the present invention desirably has a molecular weight in excess of about 600 and preferably has a molecular weight within the range of about 1,000 to 20,000 with a more preferred range of from about 1,500 to about 10,000. The amount of the polyalkylene glycol in the treating solutions will vary, depending upon the particular molecular weight of the polyalkylene glycol which,

is used. In general, it has been found that the higher the molecular weight of the polyalkylene glycol, the lower is the concentration required to produce the desired results in the treating solution. Desirably, the polyalkylene glycol is present in the treating bath in amounts within the range of about 0.001 percent by weight of the solution up to its saturation concentration in the bath, with amounts within the range of about 0.006 to 1.0 percent by weight of the solution being preferred, the higher concentrations typically being used with the lower molecular weight materials, and vice versa. Additionally, it is to be appreciated that various polyalkylene glycols may be used, such as polyethylene glycol, polypropylene glycol, polybutylene glycol, and the like. Of these, the polyethyleneglycols are generally preferred and, hence, particular reference will be made to these materials'hereinafter.

The plating solutions of the present invention also contain at least one tertiary amine compound of the structural formula that has been indicated above. Desirably, the amine compound used will be present in an amount within the range of 0.001 percent by weight of the solution up to their saturation content in the solution. Preferably, amounts of the amine compound within the range of about 0.002 to 0.1 percent b weight of the solution will be used.

Various amine compounds that may be used are as follows: triphenyl amine; tribenzyl amine; triphenethyl amine; N,N,N (4-phenyl butyl) amine; hydroxy methyl dibenzyl amine; 2-hydroxy ethyl dibenzyl amine; 4- chlorobutyl diphenyl amine; 4-iodobutyl diphenyl amine; 3-bromopropyl diphenyl amine; mono-, dior trimethyl substituted triphenyl amine; mono-, di-, or trichloro substituted tribenzyl amine, and the like.

As has been indicated herein above, the aqueous acidic plating baths of the present invention arefound to give excellent plating results even where the baths contain appreciable quantities of ferrous iron. As is recognized by those in the art, even though the baths are initially free of ferrous iron, where the baths are used to treat ferrous metal surfaces, the etching action of the bath results in the dissolution and continual build-up of ferrous iron in'the plating solution. Thus, the plating baths of the present invention may also contain ferrous iron ions in amounts up to the saturation point of the ferrous iron in the bath, with amounts of ferrous iron ions within the range of about 5 to grams per liter being typical. Where such typical amounts of ferrous iron are present in the bath, and even where the ferrous iron content is greater than the saturation point of the path, it is still found that excellent quality copper coatings can be produced.

ltis to be appreciated that although certain particular preferred ranges have been given for the concentrations of the components of the plating sotuions of the present invention, these concentrations are merely exemplary of those which may be used. Thus, in some instances, concentrations of these components which are outside of the ranges indicated may also be used to give satisfactory results. Accordingly, it is believed that those in the art will readily be able to determine the concentration of each of these components which should be used in each instance, depending upon the type of ferrous metal surface to be treated, the nature of the nonelectrodeposited copper coating which is desired, as well as the particular type and concentration of the other components in the treating solution.

It has further been found that the combination of the various components which have been set forth herein above, produces an unexpectedly improved result as compared to the results obtained when all of these materials are not present in the treating solution. This has been found to be particularly true with respect to the inclusion of the halide ions, the polyalkylene glycol and the amine components in the treating bath. Where even one of these three components is omitted from the bath, it is found that it is no longer possible to consistently obtain the bright, adherent copper coating on a wide variety of ferrous metal surfaces treated, particularly with relatively large amounts of ferrous iron present. Accordingly, it is important in the present invention to include all of these components in the copper plating bath.

1n carrying out the method. of the present invention, the ferrous metal surface to be treated, such as a length of steel wire, is first cleaned, using any suitable. cleaning techniques. Where desired, this cleaning may include acid pickling, such as .with muriatic acid, alkaline cleaning, such as with alkali metal hydroxide and/or alkali metal permanganate containing cleaners, and may include a combination of several of these cleaning or pre-treating steps. Following the 'cleaning or pretreating of the steel surface, it is brought into contact with the copper plating bath of the present invention. Depending upon the particular configuration of the ferrous surface to be treated, various contacting techniques may be utilized such as immersion, spraying, flooding, and the like. Where the ferrous surface treated is steel wire, it has generally been found to be preferable if the wire is immersed in the copper plating bath. During the immersion of the wire in the bath, the copper plating bath of the present invention is desirably maintained at a temperature within the range of about 15 to C. and preferably 24 66C. and under these preferred conditions, immersion times of from about 10 seconds to 10 minutes are typical. After removal from the copper plating solution, the ferrous metal surface may then be rinsed with water and dried.

When the ferrous surface treated in accordance with this process is steel wire, if desired, following the application of the electroless copper plate, a suitable lubricant may be applied to the coated wire to facilitate a subsequent drawing operation. Various lubricant materials, as are known to those in the art, such as numerous soap containing compositions, may be applied to the copper plated wire and this lubricant coating then dried thereon. The wire may then be subjected to the desired drawing operation and it is found that following the drawing, the copper finish on the wire is very bright and uniform and shows good adhesion. Additionally, it is found that the solutions of the present invention may also be used to form a copper coating which is useful as a lubricant material for warm forming operations, as well as a decorative copper coating.

In order that those skilled in the art may better understand the present invention and the manner in which it may be practiced, the following specific examples are given. In these examples, unless otherwise indicated, parts and percent are by weight and temperatures are in degrees centigrade.

EXAMPLE I A two liter solution was made up containing 48 grams of CuSO, 5H O, 6 grams of NaCl, 60 mls of H 80 h grams of polyethylene glycol (molecular weight 4000) and 1 percent F++ added as FeSo 7H O. Cleaned mild steel wire was processed through the bath before and after additions of N, N, N, tribenzylamine were made to the bath. The wire was processed in the bath at 100F. for two minutes. After treatment in the copper solution the wire was rinsed then dried with forced air. The N, N, N, tribenzylamine was added so that the total concentration varied from 10 mg per liter to 2000 mg per liter. Very light colored coatings with excellent adhesion were obtained at N, N, N, tribenzylamine concentrations between and 500 mg per liter. Above and below theseconcentrations the coatings were darker in color.

EXAMPLE 11 A four liter solution was made up containing 96 g of CuSO, 511 0, 120 mils. of H SO 120 mg. of N, N, N, tribenzylamine, 12 gm. of NaCl, and 1 percent Fe-las FeSO, 7H O. Polyethylene glycol (molecular weight 4000) was added to the bath in increments of gm up to a total concentration of 1 gm. Cleaned mild steel wire was processed through the bath at each increment of polyethylene glycol. The processing time was 2 minutes at 100F. The resulting-coating was examined for color and adhesion. The coatingsobtained at polyethylene glycol concentrations below 3/16 g per liter were brownish orange in color and quite porous. Adhesion was marginal. However at a concentration of g per liter of polyethylene glycol, the resulting coating was very light in color and adhesion was excellent.

EXAMPLE 111 A four liter aqueous bath containing 24 grams per liter of CuSO, 51-1 0, 30 ml/] H 80 400 g/l FeSO, 187F1 0 (8 percent Fe-H-), 3 g/l NaCl and 0.25 g/l polyethylene glycol (molecular weight 4000) was prepared. To the bath were added varying concentrations of dibenzylethanol amine such as 0, 6 g/l, 0.23 g/l and g/l.

The wire was given the following coating cycle:

l. pickle in muriatic acid (20 percent v/v) for 5 minutes at ambient temperature;

2. clean water rinse for 30 seconds;

3. clean with a commercial cleaner for 2 minutes at .4. flash pickle for 5 seconds in a 20 percent v/v muriatic acid solution;

5. clean water rinse for 15-30 seconds;

6. copper bath for 2-5 minutes at 1 10F.;

7. clean water rinse for 30 seconds;

8. forced air dry off or a 30 second clip in a soapborax lubricant with an oven bake.

After the wire was treated according to the above cycle, the results showed that maximum color and adhesion of copper occurred at a conetration of 0.25 g/l and above.

While there have been described various embodiments of the invention, the compositions and methods described are not intended to be taken as limiting the scope of the invention as changes therewith in are possible and each element in the following claims is intended to be understood as referring to all equivalent elements for accomplishing substantially the same result in substantially the same or equivalent manner, it being intended to cover the invention broadly in whatever form its principle may be utilized.

What is claimed is:

1. An aqueous acidic solution suitable for forming a copper plate on ferrous metal surfaces without the application of electric current, which comprises copper ions, halide ions, selected from chloride, bromide and iodide ions; a polyalkylene glycol selected from the group consisting of polyethylene, polypropylene and polybutylene glycols having a molecular weight in excess of about 600; and a tertiary amine of the formula:

wherein:

a is zero or 1;

b is 2 or 3;

a b is 3;

n is 0 to 4, inclusive;

R is alkyl or substituted alkyl of l to 4 carbon atoms where the substituent may be hydroxy or halo; and,

R is phenyl or substituted phenyl where the substituent may be mono-, di-, or trihalo or alkyl of 1 to 4 carbon atoms wherein the copper ions are present in an amount of about 0.1 to 3 percent by weight, the halide ions are present in an. amount within the range of about 0.001 to 10 percent by weight, the polyalkylene glycol is present in an amount of at least about 0.001 percent by weight, and the amine material is present in an amount of at least 0.001 percent by weight to saturation.

2. The composition as claimed in claim 1 wherein the polyalkylene glycol has a molecular weight within the range of about 600 to 20,000.

3. The composition as claimed in claim 1 wherein the halide ions are chloride ions.

4. The composition of claim 4 wherein b is 3.

5. The composition of claim 1 wherein R is hydroxyl alkyl of from 1 to 4 carbon atoms.

6. The composition of claim 1 wherein n is 1.

7. The composition of claim 1 wherein R is phenyl.

' 8. The composition of claim 1 wherein the amine is N, N, N-tribenzyl'amine 9. The composition of'claim 1 wherein the amine is N, N dibenzylhydroxyethyl' amine.

10. A process for forming a copper coating on ferrous metal surfaces which comprises treating the ferrous metal surface to be coated with the coating com- 13. The process of claim 10 wherein b is 3.

14. The process of claim 10 wherein R is hydroxy alkyl of from 1 to 4 carbon atoms.

15. The process of claim 10 wherein n is l.

16. The process of claim 10 wherein R is phenyl.

17. The process of claim 10 wherein the amine is N, N, N tribenzyl amine.

18. The process of claim 10 wherein the amine is N, N dibenzylhydroxyethyl amine.

19. A ferrous metal surface having a copper coating formed thereon in accordance with the method of claim 16. i

20. A ferrous metal surface having a copper coating formed thereon in accordance with the method of claim 12. 

2. The composition as claimed in claim 1 wherein the polyalkylene glycol has a molecular weight within the range of about 600 to 20,000.
 3. The composition as claimed in claim 1 wherein the halide ions are chloride ions.
 4. The composition of claim 4 wherein b is
 3. 5. The composition of claim 1 wherein R is hydroxyl alkyl of from 1 to 4 carbon atoms.
 6. The composition of claim 1 wherein n is
 1. 7. The composition of claim 1 wherein R'' is phenyl.
 8. The composition of claim 1 wherein the amine is N, N, N-tribenzyl amine.
 9. The composition of claim 1 wherein the amine is N, N dibenzylhydroxyethyl amine.
 10. A process for forming a copper coating on ferrous metal surfaces which comprises treating the ferrous metal surface to be coated with the coating composition as claimed in claim 1 and maintaining this composition in contact with the ferrous metal surface for a period sufficient to effect the formation of a copper coating.
 11. The process as claimed in claim 10 wherein the polyalkylene glycol in the copper plating composition has a molecular weight from about 600 to 20,000.
 12. The process as claimed in claim 11 wherein the halide ions in the copper composition are chloride ions.
 13. The process of claim 10 wherein b is
 3. 14. The process of claim 10 wherein R is hydroxy alkyl of from 1 to 4 carbon atoms.
 15. The process of claim 10 wherein n is
 1. 16. The process of claim 10 wherein R'' is phenyl.
 17. The process of claim 10 wherein the amine is N, N, N -tribenzyl amine.
 18. The process of claim 10 wherein the amine is N, N -dibenzylhydroxyethyl amine.
 19. A ferrous metal surface having a copper coating formed thereon in accordance with the method of claim
 16. 20. A ferrous metal surface having a copper coating formed thereon in accordance with the method of claim
 12. 